Recently, heat-sensitive recording papers have come into use as recording papers for recording facsimile output data or computer output data, utilizing the advantages of heat-sensitive recording papers, such as that they form color based on primary coloration, and that they require no developing step. Such heat-sensitive recording papers are usually referred to as "dye type", and are disclosed in Japanese Patent Publication Nos. 4160/68 and 14039/70. Japanese Patent Application (OPI) No. 27253/80 (The term "OPI" as used herein refers to a published unexamined Japanese patent application), etc.
In general, the use of a heat-sensitive recording paper as the recording paper enables to use a light and small-sized recording apparatus. Thus, heat-sensitive recording papers have recently come into increased use. On the other hand, heat-sensitive recording papers typically have the defect that the recording speed cannot be increased as high as desired due to a limited response speed of the recording element, since heat is used as the recording energy. In order to overcome this defect, various efforts have been made with respect to recording devices and recording papers. One of them is to increase smoothness of the surface of heat-sensitive recording paper, specifically to conduct calender treatment.
However, such surface treatment for imparting smoothness is accompanied by various defects.
One defect is fogging. That is, the coloration reaction takes place during the surface-treating step to cause coloration of recording paper. As an approach to overcome this problem, addition of granular wax has been proposed (Japanese Patent Publication No. 14531/75). However, waxes generally have a large heat capacity and a large heat of fusion, thus deteriorating the heat response of heat-sensitive recording paper.
Another defect of such treatment is a deterioration of writing properties with respect to pencils, ball-point pens, etc.
A third defect is a bonding phenomenon between the recording element and the recording paper in colored portions due to seriously increased adhesion between the recording element and the heat-sensitive recording paper which deteriorates running properties.
In spite of these various defects, the surface treatment at present must unavoidably be conducted for imparting smoothness due to comparatively large contribution of the improvement of smoothness to the improvement of the recording speed.